Another collecting method may be to search on Earth for these exoplanet grains. Cosmic dust
particles smaller than 10–100 \(\mu \) m survive atmospheric entry without
severe heating [1]}, and biosignatures can be preserved.
Such micrometeorites have been collected from Antarctic snow or ice
[2]}, [3]}. The accretion rate \(A_\oplus \)  estimated above
implies that \(10^9 \, \eta _{c,2}\)  grains from exoplanets are
embedded in the entire Antarctic ice (\(1.4 \times 10^7 \ \rm km^2\)  area
and 2500 m mean depth corresponding to an accumulation time of
\(\sim 3 \times 10^5\)  yr, [4]}), or \(10^2 \, \eta _{c,2}\) 
grains in an area of \(1 \ \rm km^2\) . Cosmic dust particles have also been
collected in deep-sea sediments, where low accumulation rates and
long exposure times allow particles to collect in
high concentrations [5]}. For a typical accumulation
rate (\(2 \times 10^{-6}\)  m/yr), about \(10^4 \, \eta _{c,2}\)  grains from
exoplanets can be collected from deep-sea clay of 1 m depth
(corresponding to \(5 \times 10^5\)  yr) in a \(100 \ \rm km^2\) 
area. It is worth investigating the best locations and strategies to collect these extremely rare
particles on Earth by future technologies.
